The term "oil shale", as used herein, refers to a carbonaceous rock, i.e., Devonain marine composition, particularly Eastern oil shale, that contains a high molecular weight organic polymer called kerogen. Kerogen is the oil precurser in the oil shale rock. To extract kerogen from oil shale, the oil shale is generally first crushed into small pieces and heated in retorts to pyrolysis temperatures in the range between about 500.degree. F. to about 1200.degree. F. Retorting of the oil shale at pyrolysis temperatures causes decomposition of the kerogen and evolution of shale oil trapped in the matrix of the ore, in the form of a vapor which can be subsequently condensed to form usable shale oil liquid.
A number of different retorting apparatus and processes are known for treatment of Eastern oil shale to evolve shale oil therefrom. Some of the major shale oil retorting systems as well as lesser known processes are discussed in U.S. Pat. No. 4,410,416 to Karl Everman, the disclosure of which is incorporated herein by reference in its entirety. Generally speaking, however, the major shale oil retorting processes utilize either a hot gas as the heating medium circulating within a drum containing the shale particles or a hot liquid into which the particles are dumped for a considerably large residence time as compared to the present invention. Following immersion in the hot liquid, the particles must then be separated from the hot liquid in an expensive and time-consuming process, such as by rotating the drum in which the particles have been retorted so that the particle material can be dispensed by gravity through a stationary outlet.
The aforesaid prior art Everman patent discloses a split hub wheel apparatus allowing shale particles to be loaded into spoke-like containers of the wheel, dipped into a hot oil bath that enters the containers through perforations and subsequently unloaded after shale oil vapor is evolved as a result of dipping the materials in the bath. However, the prior art Everman split hub wheel can only function as a batch processing unit which sharply increases the production time required to evolve a particular quantity of shale oil vapor from the shale particles.
Another drawback of the prior art Everman apparatus is the strict requirement that shale oil retorting occurs within an airtight retort, requiring the use of expensive seals. To a large extent, safe operation of the Everman retort depends upon the integrity of the seals; if the seals fail and air comes into contact with the hot oil used in the liquid bath, an explosion would necessarily result.
Another drawback of the prior Everman retort is the requirement that a large number of feed and discharge pipes, and moving parts be present in the hostile environment, of the retort which may be adversely effected thereby. For example, in the prior Everman apparatus, shale is augered into the split wheel hub within the retort for loading into the spoke containers. Since the auger is sealed to prevent air from entering the split hub wheel retort, the hot gaseous environment within the retort tends to come into contact with the auger seal causing degradation thereof. Too, by augering the raw shale particles into the split wheel hub, the particles are unnecessarily subjected to severe agitation which tends to increase the production of fines collecting as a sludge within the hot oil bath.
It is accordingly an object of the present invention to provide a novel oil shale retorting system capable of retorting shale in a continuous feed process to obtain high production yields of shale oil in a safe and efficient manner.
Another object of the invention is to provide a method and apparatus providing a direct flow path for enabling evolved shale oil vapor to quickly exit from the retort for condensation into liquid form to minimize the presence of the flammable shale oil vapor within the retorting system.
Still another object is to provide a retorting structure and novel process oil wherein vapors of the process oil produced during the retorting process are subjected to fast refluxing action to minimize the presence of flammable vapors within the retort.
Yet a further object of the present invention is to provide a retorting apparatus and method which does not require retorting to occur under air-tight conditions, without sacrificing safety.
Still a further object is to provide a continuous feed conveyor within the retorting system that features a minimum of moving parts within the rugged and hostile environment prevailing in the retort housing.